The present invention relates to a beam shape compensation optical system for compensating a cross-sectional shape of a beam, and an imaging device employing the beam shape compensation optical system.
Among devices utilizing light beams, some require a beam of which a cross sectional shape is compensated. For example, in an imaging device utilizing a scanning beam, it is preferable that a beam spot formed on a surface on which an image is formed has a circular shape. Therefore, the cross-sectional shape of a beam emitted by a light source such as an argon laser source is compensated to have a circular cross section.
Conventionally, such compensation is done at a designing and/or manufacturing stage. Optionally or alternatively, a compensation optical system such as a zoom expander including a plurality of cylindrical lenses or the like is adopted to compensate the shape (i.e., to compensate to have the circular cross section) of the beam.
In order to design and manufacture an optical system which is capable of compensating a laser beam as desired, the optical system should be designed for individual devices since the cross sectional shape of the laser beam emitted by the laser sources have individual differences. Further, even in a single device, if the laser source is replaced with another one, the compensation optical system should also be replaced according to the characteristic of the new laser source.
If the zoom expander is used, a relative inclination between the generating lines of the respective cylindrical lenses greatly affect wavefront aberration. Therefore, when the zoom expander is used, a troublesome adjustment of the zoom expander is required. Further, decentering of the cylindrical lenses when zooming is performed also causes a relatively large amount of aberration. Therefore, the compensation of the cross-sectional shape of the beam by the zoom expander is very difficult.